This invention relates to a shield tunneling method and a machine therefor, which excavate a tunnel by causing a pressure to act on the tunnel face, while preventing collapse of the tunnel face, the pressure being such a level as balances an earth pressure and underground water pressure in the face ground.
One of the known methods of preventing collapse of the tunnel face in excavating a tunnel is to apply a pressure with sludge, such as bentonite slurry, to the face, as disclosed in U.S. Pat. No. 3,946,605. The other method is to apply a pressure to the face with muck from the tunnel face, as disclosed in U.S. Pat. No. 4,167,289.
The former can effectively resist the underground water, but, in the ground of a high permeability, such as sandy ground, can not independently resist the face earth pressure. The latter has been difficult in resisting a water pressure in the ground in which the underground water level is high.
With a view to solving the drawback of the conventional method and machine, it is an object of the present invention to provide tunneling method and machine for excavating a tunnel against an earth pressure and a water pressure in the face ground while maintaining the face stable, irrespective of the nature of soil in the face ground or the underground water level being high or low.
Regarding stability of the tunnel face, the inventor came to such a conclusion to be described below. If the mined material or muck from the tunnel face is directly urged against the tunnel face so that a muck pressure can balance the earth pressure in the tunnel face, then the tunnel face becomes stabilized as in the ground under the natural condition. On the other hand, a liquid is pressurized to such a level as making an equilibrium with the level of the underground water pressure, so as to resist the underground water, and to impede movement of the underground water. The underground water thus can be maintained in a condition similar to the natural condition. By the use of the muck and liquid which are pressurized to such a level as balancing the earth pressure in the face ground and the underground water pressure, stability of the tunnel face is extremely rationally maintained. If the muck alone can be taken out of the tunnel face, without taking underground water out of the tunnel face or moving same, then excavation of a tunnel can be safely and efficiently proceeded with, without impairing stability of the tunnel face.
In accordance with the theory described above, improvements in a conventional shield tunneling method and machine are made, for attaining the object described above.